1. Field of Invention
The present invention relates generally to the field of wireless communication systems and, more particularly, to electronic circuits in wireless communication systems.
2. Discussion of Related Art
Wireless communications systems generally have separate high-band and low-band interfaces, or in the case of multi-mode systems, separate mode interfaces, between the transceiver transmitter output and the inputs of the power amplifier. For example, a dual-mode wireless communication system would have separate interfaces for the GMSK/EDGE (Gaussian Minimum Shift Keying/Enhanced Data Rates for GSM Evolution) mode and the WCDMA (Wideband Code-Division Multiple Access) mode. If the interfaces are differential, then for a dual-band or dual-mode system, four different radio frequency (RF) routes and two RF baluns are required.
As known to those skilled in the art, a balun is a passive electronic device that converts between balanced and unbalanced electrical signals and which may also change impedance. The function of the balun is to achieve compatibility between different systems within the wireless communication system or network. Accordingly, they are widely used in many different applications including mobile telephone networks, radio systems, television systems, radars, and the like. For example, in television, radio and other antenna installations, baluns are used to convert between 300 Ohm ribbon cable (balanced) and 75 Ohm coaxial cable (unbalanced) or to directly connect a balanced antenna to an unbalanced coaxial cable. Similarly, in electronic communications systems, baluns are used to convert Twinax cables to Category 5 or 6 cables, and back, or to convert between coaxial cable and ladder line. Baluns involve some form of electromagnetic coupling to achieve the conversion, and therefore, are commonly implemented using transformers.